# 4th Grade - Prime Numbers

 Grade Level: 4th Skill: Numbers - large, small, prime and negative Topic: Prime Numbers Goal: Know that numbers such as 2, 3, 5, 7, and 11 do not have any factors except 1 and themselves and that such numbers are called prime numbers. Skill Description: Identify numbers that can only be divided by one and themselves (i.e. 2, 3, 5, 7, 11, 13…)

## Building Blocks/Prerequisites

### Sample Problems

(1)

Write the factors for the number below. Is it prime or composite?

27: __________ _____________

(1, 3, 9, 27; composite)

(2)

Which number is not prime:

2, 3, 7, 13, 19, 21, 23

List the factors for the composite number: _______________________

(21; Factors: 1,3,7,21)

(3)

Which array does not relate to the product 16:

(a)

 4 4

(b)

 8 2

(c)

 1 6 1

(d)

 6 3

(d)

(4)

Complete the factor tree:

81

/ \

__ x __

/ \ / \

__ x __ __ x __

Write the prime numbers ___________________

(3 x 3 x 3 x3 =81)

(5)

Complete the factor tree:

56

/ \

__ x __

/ \ / \

__ x __ __ x __

Write the prime numbers _____________

(2 x 2 x 2 x 7= 56)

### Learning Tips

(1)

Multiplication table:

Teach child to use the multiplication table to help find multiples and factors.

 0 1 2 3 4 5 6 7 8 9 0 0 0 0 0 0 0 0 0 0 0 1 0 1 2 3 4 5 6 7 8 9 2 0 2 4 6 8 10 12 14 16 18 3 0 3 6 9 12 15 18 21 24 27 4 0 4 8 12 16 20 24 28 32 36 5 0 5 10 15 20 25 30 35 40 45 6 0 6 12 18 24 30 36 42 48 54 7 0 7 14 21 28 35 42 49 56 63 8 0 8 16 24 32 40 48 56 64 72 9 0 9 18 27 36 45 54 63 72 81

(2)

Arrays:

Review how to use arrays- the number of boxes shaded across (10) is one factor and the number of boxes shaded going down is another factor (4). There are 40 boxes completely shaded (4 x 10 = 40).

 10 4

How to make arrays on the graph paper template:

• Highlight the boxes desired

• Click on format

• Click on borders and shading

• Fill with color preference

(3)

Math vocabulary:

Prime number- a number that only has two factors (1 and itself; For example, 3 only has two factors 1 x 3. Therefore, 3 is a prime number).

Composite number- a number that has more than two factors.

Factor Tree- A diagram that helps find prime factors of a product.

Product

/ \

factor x factor

/ \

__x __

12

/ \

6 x 2

/ \

2 x 3

1” is neither prime nor composite

(4)

Explain how to use factor trees:

Reminder: There can be various ways to begin the factor tree, as long as children get the same result of prime numbers at the end of the tree (highlighted numbers).

12

/ \

6 x 2

/ \

2 x 3

Write the product of prime numbers as: 2 x 2 x 3 = 12

OR

12

/ \

4 x 3

/ \

2 x 2

Write the product of prime numbers as: 2 x 2 x 3 =12

(5)

Practice basic multiplication and division facts:

Child will be more accurate and quick in determining factors for products.

### Extra Help Problems

(1)

List the factors for the number below. Label prime or composite.

20: ________________ _____________

(1,2,4,5,10,20; composite)

(2)

List the factors for the number below. Label prime or composite

25: ________________ _____________

(1,5,25; composite)

(3)

List the factors for the number below. Label prime or composite

31: ________________ _____________

(1,31; prime)

(4)

List the factors for the number below. Label prime or composite

9: ________________ _____________

(1,3,9; composite)

(5)

List the factors for the number below. Label prime or composite

58: ________________ _____________

(1,2,29,58; composite)

(6)

Make an array for: 27

Label prime or composite: ________________

(Arrays can be 1x27 or 3x9; composite)

(7)

Make an array for: 35

Label prime or composite: ___________________

(Array can be1x35 or 5x7; composite)

(8)

Make an array for: 19

Label prime or composite: _________________________

(Array 1x19; prime)

(9)

Make an array for : 121

Label prime or composite ___________________

(Array can be 1x121 or 11x 11)

(10)

Make an array for : 8

Label prime or composite _______________________

(Arrays can be 1 x 8 or 2 x 4; composite)

(11)

Use a factor tree to find the prime factors for the product:

75

/ \

__ x __

/ \ / \

__ x __ __ x __

Write the prime factors as a product ___________________

(3 x 5 x 5 = 75)

(12)

Use a factor tree to find the prime factors for the product:

57

/ \

__ x __

/ \ / \

__ x __ __ x __

Write the prime factors as a product ___________________

(3 x 19 =57)

(13)

Use a factor tree to find the prime factors for the product:

98

/ \

__ x __

/ \ / \

__ x __ __ x __

Write the prime factors as a product ___________________

(2 x 7 x 7 =98)

(14)

Use a factor tree to find the prime factors for the product:

60

/ \

__ x __

/ \ / \

__ x __ __ x __

Write the prime factors as a product ___________________

(2 x 2 x 3 x 5= 60)

(15)

Use a factor tree to find the prime factors for the product:

22

/ \

__ x __

/ \ / \

__ x __ __ x __

Write the prime factors as a product ___________________

(2 x 11 =22)

(16)

Use a factor tree to find the prime factors for the product:

56

/ \

__ x __

/ \ / \

__ x __ __ x __

Write the prime factors as a product ___________________

(2 x 2 x 2 x 7=56)

(17)

Use a factor tree to find the prime factors for the product:

113

/ \

__ x __

/ \ / \

__ x __ __ x __

Write the prime factors as a product ___________________

(1 x 113)

(18)

Write the missing prime factor:

11 x 2 x ___ = 66

(3)

(19)

Write the missing prime factor:

2 x 2 x 2 x ___ x 5 = 120

(3)

(20)

Write the missing prime factor:

5 x ___ = 155

(31)

(21)

Which is a prime number:

1. 4

2. 52

3. 39

4. 37

(37)

(22)

Which number is not a factor of 12:

1. 3

2. 6

3. 8

(8)

(23)

Which equations shows prime factors of 32:

1. 8 x 2 x 2

2. 2 x 2 x 2 x 3

3. 2 x 2 x 2 x 2 x 2 x 2

(c)

(24)

What type of number is 1:

1. prime

2. composite

3. both

4. neither

(d)

(25)

What is the product for:

2 x 2 x 3 x 11 = ______

(132)